Circuit arrangement, switching module comprising said circuit arrangement and use of said switching module

ABSTRACT

Circuit array, circuit module with the circuit array, and use of the circuit module The invention relates to a circuit array with an antenna input ( 1 ), a signal input ( 2 ) and a signal output ( 3 ), a switch unit ( 4 ), in which the antenna input ( 1 ) is connected to a first protective device ( 6 ) against electrostatic discharges, wherein the first protective device ( 6 ) is a band-pass filter in a T configuration. An advantage of the first protective device ( 6 ) is that when it is used in a mobile telephone, a band-pass filter in the front-end module can be omitted. In addition, the band-pass filter has very favorable filtering characteristics, so that ESD-related interference can be effectively suppressed. The invention also relates to a circuit module and use of the circuit module.

[0001] The invention relates to a circuit array, which has an antennainput, a signal input and a signal output. In addition, the circuitarray has a switch unit that optionally connects the antenna input withthe signal input or the signal output.

[0002] Circuit arrays of the type mentioned above are often used asmulti-band front-end modules for mobile telephones. In this application,they are connected to the antenna of a mobile telephone at the antennainput. When the antenna comes into contact with an electrically-chargeduser, this can result in electrostatic discharge, also known under thename “electrostatic discharge (ESD).” These electrostatic discharges cancreate voltage peaks that are capable of destroying the circuit array.Thus, it is necessary to equip circuit arrays of the type mentionedabove with a device that protects against ESD.

[0003] Printed specification WO 00/57515 discloses circuit arrays of thetype mentioned above that are equipped with a protective device againstESD. The protective device comprises an electric high-pass filter inwhich a capacitor is connected in series and an inductor is connected inparallel to the antenna input path.

[0004] A drawback of the known circuit array is that the ESD protectivedevice only helps reduce the ESD impulse entering the circuit arraydirectly through the antenna. In addition to the impulse entering thecircuit array directly through the antenna, an electrostatic dischargecan also generate a high voltage in the circuit array through groundcoupling. This can occur, for example, because the control inputnormally used in a circuit is arranged either on the high voltage (high)or on a low voltage (low). In this case, the high voltage (high) isdefined, for example, by the fact that it lies 2.3 V above the groundvoltage of the circuit array. Because, in the case of a mobiletelephone, as with many other devices based on signal transmission viaantennas, the signal input runs from the antenna to the system's ground,an electrostatic discharge can also directly affect the ground voltageof the circuit array in a circuit array of the type mentioned above. Asa result of the directly coupling of a control line to ground throughthe “high” condition, the voltage impulse resulting from anelectrostatic discharge can not only affect the path, via the antenna,but also the circuit array, via the control line. The known circuitarray is not protected against these effects.

[0005] In addition, the high-pass filter used in the known circuit arrayhas the characteristic of being a very simply designed filter thatallows all frequency components of a signal, beginning with a certaincutoff frequency, to pass through it virtually unimpeded. In general,however, only a very narrow frequency range is relevant to the furtherprocessing of the signal received by the antenna in the mobiletelephone. For example, frequencies of between 1 and 2 GHz are used inmobile telephones based on the GSM, PCN, or PCS standard. All otherfrequencies received by the antenna tend to be interfering and,therefore, must be filtered out. Accordingly, at least one band-passfilter is needed to make the signal captured by the circuit arraymentioned above capable of being processed for a mobile telephone. Thehigh-pass filter arranged in the known circuit array can only cut offfrequencies below a certain cutoff frequency. For this reason, at leastone filter circuit must be connected downstream from this filter, inorder to remove the frequency range relevant to the mobile telephonefrom the signals received by the antenna.

[0006] Accordingly, an advantage of the known circuit array is that thehigh-pass filter circuit used to protect against ESD has an insertionloss, causing the wanted signals to undergo a certain attenuation,although cutting of the transmitted frequency band does not take place.Accordingly, a disadvantage of the known circuit array is a generallyhigh insertion loss.

[0007] The goal of this invention, therefore, is to provide a circuitarray of the type mentioned above, in which the frequency dependency ofthe protective device at the antenna input is improved.

[0008] This goal is achieved through a circuit array according to claim1. Additional advantageous embodiments of the invention, as well as acircuit module and the use of the circuit module can be seen from thedependent claims.

[0009] A circuit array is described which contains a switch unit with anantenna input, a signal input, and a signal output. The switch unit issuitable for electrically connecting the antenna input with either thesignal input or the signal output. In addition, a control line thatcontrols the switch position in the switch unit can be arranged at theswitch unit. Additionally, the antenna input is connected to a firstprotective device against electrostatic discharges.

[0010] The first protective device against electrostatic discharges isimplemented in the form of a band-pass filter in a T configuration.

[0011] The advantage of a band-pass filter is that it has a highinsertion loss below a first cutoff frequency and above a second cutofffrequency. As a result, frequencies can be effectively suppressed,especially low frequencies that contain the bulk of electrical output ofthe impulses generated by electrostatic discharge. By arranging aband-pass filter at the antenna input, at least the need for subsequentfilters in the reception paths can be loosened, which results in agenerally improved insertion loss.

[0012] In an advantageous embodiment of the invention, the firstprotective device has an antenna input and a switch output. The antennainput and switch output are connected to one another by a line. A firstseries circuit comprising an inductor and a capacitor is connected inseries to a second series circuit comprising an inductor and a capacitorand is connected in series to the line. Between these two seriescircuits, a parallel circuit comprising an inductance with a capacitorwith a ground is connected to the circuit array in parallel to the line.

[0013] A band-pass filter in a T configuration is achieved with thecircuit array of the protective device described above.

[0014] To use the circuit array of the invention in a mobile telephonein which frequencies based on the GSM or PCS standard are used, it isadvantageous for the band-pass filter to have an attenuation less than0.5 dB between 1 and 2 GHz. Outside this frequency range, the band-passfilter should have the highest possible attenuation (e.g. >20 dB atf>3.4 GHz).

[0015] The circuit array of the invention, together with the band-passfilter, is also advantageous in that, as a result of the two capacitorsconnected in series to the line, a DC voltage block is achieved thatprevents DC voltage applied to the switch unit from being discharged tothe ground. This effectively reduces the risk of a short circuit.

[0016] In an advantageous embodiment of the invention, the control lineis also connected to a second protective device against electrostaticdischarges. The advantage of this arrangement is that ESD interferencepenetrating into the circuit can be effectively prevented through groundcoupling via the control line.

[0017] The protective devices against electrostatic discharges areadvantageously connected to a ground connection, into which the excessvoltage from the electrostatic discharges can be discharged.

[0018] The switch unit can, for example, be a voltage-controlled switch,such as the type normally used in mobile telephone because of its lowpower consumption. In particular, a gallium-arsenide switch can be usedas the switch unit.

[0019] The switch unit can also have multiple signal inputs and outputs.Accordingly, multiple control lines are needed.

[0020] The circuit array can also be provided with a decoder, which canbe used to reduce the number of control lines. Such a decoder normallyrequires a power supply, which is connected via a supply line. The ESDprotection of such a circuit can be improved even further by connectingthe supply line to a third protective device against electrostaticdischarges.

[0021] The decoder can also be designed so that the voltages of thecontrol lines are generated from the voltage of the supply line.

[0022] This can be accomplished by means of so-called “pull-upresistors,” for example. Then ESD protection can be simplified byproviding only the power supply line with a second protective device. Inthis case, protection of the control lines is provided through theprotection of the power supply.

[0023] The circuit array can also contain frequency filters that areassigned to individual signal inputs or signal outputs. They areespecially suitable for filtering the frequencies received by theantenna on a mobile telephone in such a way that the signals conductedand filtered through the signal output can be processed further by themobile telephone. The same applies to the signal inputs of the circuitarray, which, in a mobile telephone, are used to transmit the voicesignals generated in the mobile telephone to a receiver via the antenna.

[0024] The use of a voltage-limiting element, which is connected inparallel to the control line and is also connected to the groundpotential, represents another option for a second protective deviceagainst electrostatic discharges. A voltage-limiting element can be avaristor, for example. A varistor has very low resistance beginning at acertain cutoff voltage, so that excess voltage against ground can bediverted. Varistors with low switching voltage are especially suitable,because this minimizes the residual voltage that occurs in a voltageimpulse and loads the circuit array. For this reason, it is advisable touse varistors with a varistor voltage of between 4 and 20 V.Accordingly, the terminal voltage in a voltage impulse that loads thecircuit array is about 8 to about 50 V. As a result, the circuit arraycan be reliably protected against destruction in the event of an ESDimpulse.

[0025] Another possibility is to use a switch spark gap or a Z-diode asa second protective device against electrostatic discharges.

[0026] The invention also specifies a circuit array in which the antennainput is connected to an antenna, in which the signal output isconnected to a receiving amplifier of a mobile telephone, and in whichthe signal input is connected to a transmission amplifier of a mobiletelephone.

[0027] In addition, a circuit module is specified which contains acircuit array according to the invention. The circuit module alsocontains a multilayer ceramic substrate with integrated passivecomponents, which form electric frequency filters. These frequencyfilters are assigned to the signal inputs or outputs. The switch unit,which can, for example, be implemented with the aid of PIN diodes or inthe form of a gallium-arsenide switch, is arranged on the upper side ofthe multilayer ceramic substrate. In addition, the first and, ifapplicable, second protective device against electrostatic discharges isintegrated into the circuit module.

[0028] An advantage of the circuit module is that, as a result of theintegration of the passive components into the ceramic substrate, aswell as the integration of the protective device into the circuitmodule, a high degree of integration is achieved, which advantageouslyaffects the space requirements of the circuit module. The integration ofthe first and, if applicable, second protective device into the circuitmodule can occur, for example, by mounting these components onto thesurface of the ceramic substrate, adjacent to the switch unit.

[0029] In particular, it is also advantageous to use the circuit moduleas a front-end module in a mobile telephone.

[0030] In the following, the invention is explained in greater detail onthe basis of example embodiments and the corresponding diagrams.

[0031]FIG. 1 shows, as an example, a circuit array according to theinvention in a basic circuit diagram.

[0032]FIG. 2 shows, as an example, another circuit array according tothe invention in a basic circuit diagram.

[0033]FIG. 3 shows, in a basic circuit diagram, the use of the circuitarray according to the invention in a mobile telephone.

[0034]FIG. 4 shows, as an example, the circuit module according to theinvention in a schematic longitudinal section.

[0035] The same reference symbols refer to the same elements in alldiagrams.

[0036]FIG. 1 shows a circuit array with a switch unit 4, which isprovided with a ground 8. The switch unit 4 has an antenna input 1,which is connected to an antenna 18. The antenna input 1 is connected toa first protective device 6 against electrostatic discharges (indicatedby the lighting symbol in FIG. 1). The switch unit 4 contains at leastone control line 5, which controls the switching process for connectingthe antenna input 1 with the signal inputs 2 or the signal outputs 3 ofthe switch unit 4. Three control lines 5 are shown in FIG. 1. At leastone of these control lines is provided with a second protective device 7against electrostatic discharges. These second protective device 7 isimplemented in the form of a varistor, which is connected to the ground8.

[0037] The switch unit 4 depicted in FIG. 1 also has a decoder, forwhich a supply line 11 is required. The supply line 11 is connected to asupply voltage +Vcc. In addition, the supply line 11 is connected to athird protective device 12 against electrostatic discharges. The thirdprotective device 12 can, for example, be a varistor that is connectedto the ground 8.

[0038] The first protective device 6 is implemented in the form of aband-pass filter in a T configuration. It has an antenna input 111 and aswitch output 112. The antenna input 111 and the switch output 112 areconnected to one another by a line 113. A series circuit 114, comprisingan inductor L1 and a capacitor C1, as well as a second series circuit115, comprising an inductor L2 and a capacitor C2, are connected inseries to this line 113. Between the two series circuits 114, 115, aparallel circuit 116 comprising and inductor L3 and a capacitor C3 isconnected in parallel to the line 113. The parallel circuit 113 isconnected to the ground 8.

[0039] Such a filter can have the following component data:

[0040] L1=from 0.1 to 22 nH

[0041] L2=from 0.1 to 22 nH

[0042] L3=from 0.1 to 22 nH

[0043] C1=from 0.1 to 18 pF

[0044] C2=from 0.1 to 18 pF

[0045] C3=from 0.1 to 18 pF

[0046] The capacitor C3 can also be replaced with a protective element,such as a varistor. Individual or multiple combinations LiCi can also beformed by transmission lines that are coupled together.

[0047]FIG. 2 shows a voltage-controlled GaAs switch 9 with an antennainput 1, to which an antenna 18 is connected. The GaAs switch 9 hastransmitter inputs TX₁ and TX₂, and receiver inputs RX₁, RX₂, and RX₃.The GaAs switch 9 is controlled through control inputs S₁, S₂, S₃, S₄,and S₅. Control takes place in that exactly one of the control inputsS₁, S₂, S₃, S₄, and S₅ is set to “high,” while the remaining controlinputs are set to “low.” The number of inputs needed can be reducedusing the decoder 10 connected to the GaAs switch 9. The decoder 10 canbe a 1-decoder or a 5-decoder, for example. It has control inputs E₁,E₂, and E₃, as well as control outputs A₁, A₂, A₃, A₄, and A₅. Thecontrol outputs A₁, A₂, A₃, A₄, and A₅ are connected to the controlinputs S₁, S₂, S₃, S₄, and S₅ of the GaAs switch 9 through connectionlines 24.

[0048] The control inputs E₁, E₂, and E₃ of the decoder 10 are connectedto the control lines 5.

[0049] An example of the decoding of a logical signal applied to one ofthe inputs E₁, E₂, and E₃ of the decoder 10 into signals applied to thecontrol inputs S₁, S₂, S₃, S₄, and S₅ of the GaAs switch 9 that aresuitable for controlling the GaAs switch is described by the followingtranslation table: TABLE 1 Logical states of the control inputs S₁, S₂,S₃, S₄, and S₅ as a factor of the logical states at the control inputsE₁, E₂, and E₃. 1 signifies “high” and 0 signifies “low.” E₁ E₂ E₃ → S₁S₂ S₃ S₄ S₅ 0 0 0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 1 0 0 0 1 1 0 0 01 0 1 0 0 0 0 0 0 1

[0050] In this case, the transmitter inputs TX₁, TX₂ correspond to thesignal inputs from FIG. 1. The receiver inputs RX₁, RX₂, and RX₃correspond to the signal outputs 3 from FIG. 1.

[0051]FIG. 3 depicts a circuit module with a GaAs switch 9, which has anantenna input 1 as well as two signal inputs 2 and three signal outputs3. In addition, the circuit module has two low-pass filters 13, 14,wherein the low-pass filter 13 can be configured for the GSM frequencyband and the low-pass filter 14 for the PCN/PCS frequency band. The GaAsswitch 9 optionally connects one of the inputs/outputs 2, 3 with itsantenna input 1. The circuit module also has band-pass filters 15, 16,17, which are connected to the signal outputs 3. The band-pass filter 15is adjusted to the GSM frequency, the band-pass filter 16 to the PCNfrequency, and the band-pass filter 17 to the PCS frequency.

[0052] The band-pass filter 15, 16, 17 at the signal output 3 can bedesigned to be less demanding in terms of its specifications, because aportion of filtration is assumed by the ESD protective device. Thisimproves insertion loss on the whole.

[0053] The signal inputs 2 of the GaAs switch 9 are electricallyconnected to transmitter amplifiers 19. The transmitter amplifiers 19,like the low-pass filters 13, 14, are adjusted to radio frequencies GSMand PCN/PCS, respectively. The signal outputs are electrically connectedto receiver amplifiers 19 a through the band-pass filters 15, 16, 17,wherein the receiver amplifiers 19 a are adjusted to the frequency bandsGSM, PCN and PCS, respectively. The antenna input 1 of the GaAs switch 9is connected to an antenna 18. The signals received by the antenna 18can now be fed, by means of the GaAs switch 9, into the band-pass filter16, the band-pass filter 17 or the band-pass filter 18, where they arefiltered according to the radio frequency used and further processed inamplifiers 19 a. The signals supplied by the transmitter amplifiers 19are filtered by the low-pass filters 13, 14 and optionally supplied tothe antenna 18 for transmission of a signal.

[0054]FIG. 4 shows a circuit module with a multilayer ceramic substrate20, into which passive components 21, 22, 23 are integrated. Thesepassive components 21, 22, 23 can be resistors, capacitors 22, andinductors 23, for example. The multilayer ceramic substrate 20 can bedesigned in a known manner. Stacked ceramic layers 30 separated bymetallic layers 31 can be used as the multilayer ceramic substrate 20. Afew of the metallic layers 31 are connected to one another throughcontinuous contacts 32 running inside the ceramic layers 30. A switchunit 4, which, for example, can be a gallium-arsenide multiple switchassembled in flip chip technology, is mounted on the upper side of theceramic substrate 20.

[0055] The switch unit 4 can, for example, be secured and electricallycontacted by means of gluing and additional wire-bonding. A GaAsmultiple switch is preferably used as the switch unit 4. This type ofswitch can have an insertion loss of 0.8 dB in the frequency rangebetween 1 and 2 GHz. It can be an integrated circuit with FET producedon a gallium-arsenide base, with its pin surfaces connected to theceramic substrate 20 by soldering.

[0056] The switch unit 4 can also be attached to the multilayer ceramicsubstrate 20 and electrically bonded by means of wire bonding. Bondingby means of soldering is preferred when the switch unit 4 is to be usedwith an additional housing.

[0057] The passive components 21, 22, 23 can form the filters 13, 14,15, 16, 17 required in accordance with FIG. 3.

[0058] In addition the switch unit 4, the first protective device 6 andthe second protective device 7 are also mounted onto the surface of thesubstrate 20. This accomplishes a high degree of integration for thecircuit module according to the invention, which advantageously affectsthe space requirements of the circuit module.

[0059] The individual components of the first protective device 6 can bearranged on the upper side of the ceramic substrate 20. However,individual components, such as the capacitors C1, C2, C3, can also beintegrated into the ceramic substrate 20, like the passive components21, 22, 23.

[0060] The invention is not limited to the examples of the second andthird protective device mentioned above; instead, all conceivableprotective device can be used in the circuit array of the invention. Inaddition, the circuit array or the circuit module is not limited toapplications in mobile telephones.

[0061] List of Reference Symbols

[0062]1 Antenna input

[0063]2 Signal input

[0064]3 Signal output

[0065]4 Switch unit

[0066]5 Control line

[0067]6, 7, 12 First, second, third protective device

[0068]8 Ground

[0069]9 Gallium-arsenide switch

[0070]10 Decoder

[0071]11 Supply line

[0072]13, 14 Low-pass filter

[0073]15, 16, 17 Band-pass filter

[0074]18 Antenna

[0075]19 Transmitter amplifier

[0076]19 a Receiver amplifier

[0077]20 Multilayer ceramic substrate

[0078]21 Resistor

[0079]22 Capacitor

[0080]23 Inductor

[0081]24 Connection line

[0082]30 Ceramic layers

[0083]31 Metallic layers

[0084]32 Continuous contacts

[0085] TX₁, TX₂ Transmitter inputs

[0086] RX₁, RX₂, RX₃ Receiver inputs

[0087] S₁, S₂, S₃, S₄, S₅ Control inputs of the switch

[0088] A₁, A₂, A₃, A₄, A₅ Control outputs of the decoder

[0089] E₁, E₂, E₃ Control inputs of the decoder

[0090] Vcc Supply voltage

[0091]111 Antenna input

[0092]112 Switch output

[0093]113 Line

[0094]114 Series circuit

[0095]115 First parallel circuit

[0096]116 Second parallel circuit

[0097] C1, C2, C3 Capacitors

[0098] L1, L2, L3 Inductors

1. A circuit array with an antenna input (1), a signal input (2) and asignal output (3), with a switch unit (4), which can optionally connectthe antenna input (1) to the signal input (2) or the signal output (3),in which the antenna input (1) is connected to a first protective device(6) against electrostatic discharges, and in which the first protectivedevice (6) is a band-pass filter in a T configuration.
 2. A circuitaccording to claim 1, in which the first protective device (6) has anantenna input (111) and a switch output (112) connected to the antennainput (1), which are connected to one another by a line (113), in whicha first series circuit (114) comprising an inductor (L1) and a capacitor(C1) is connected in series to a second series circuit (114) comprisingan inductor (L2) and a capacitor (C2) and is also connected in series tothe line (113), and in which a parallel circuit (116) comprising aninductor (L3) and a capacitor (C3) is connected between the seriescircuits (114, 115), in parallel to the line (113), and to a ground (8).3. A circuit array according to one of claims 1 or 2, in which theband-pass filter has an attenuation <0.5 dB between 1 and 2 GHz and, forfrequencies >3.4 GHz, an attenuation >20 dB.
 4. A circuit arrayaccording to one of claims 1 to 3, which has a control line (5) forcontrolling the switch unit (4) and in which the control line (5) isconnected to a second protective device (7) against electrostaticdischarges.
 5. A circuit array according to claim 4, in which theprotective devices (6, 7) are connected to a ground (8).
 6. A circuitarray according to one of claims 1 to 5, in which the switch unit (4) isa voltage-controlled switch.
 7. A circuit array according to claim 6, inwhich the switch unit (4) is a gallium-arsenide switch (9).
 8. A circuitarray according to one of claims 1 to 7, in which, additionally, adecoder (10) is provided which has a supply line (11), and in which thesupply line (11) is provided with a third protective device (12) againstelectrostatic discharges.
 9. A circuit array according to one of claims1 to 8, which additionally contains frequency filters (13, 14, 15, 16,17), each of is assigned to a signal input (2) or a signal output (3)and is connected in series to it.
 10. A circuit array according to oneof claims 1 to 9, in which the second protective device (7) contains avoltage-limiting element.
 11. A circuit array according to claim 10, inwhich the voltage-limiting element is a varistor, a spark gap or aZ-diode.
 12. A circuit array according to claim 11, in which thevaristor has a switching voltage less than 6 V.
 13. A circuit arrayaccording to one of claims 1 to 12, in which the antenna input (1) isconnected to antenna (18), the signal input (2) to a transmissionamplifier (19), and the signal output (3) to a reception amplifier (19a).
 14. A circuit array according to one of claims 1 and 3 to 13, inwhich the first protective device (6) is at least partly constructed ontransmission lines that are coupled together.
 15. A circuit arrayaccording to claim 1, in which the first protective device (6) has anantenna input (111) and a switch output (112) connected to the antennainput (6), which are connected to one another by a line (113), in whicha first series circuit (114) comprising an inductor (L1) and a capacitor(C1) is connected in series to a second series circuit (114) comprisingan inductor (L2) and a capacitor (C2) and is also connected in series tothe line (113), and in which a parallel circuit (116) comprising aninductor (L3) and a protective element is connected between the seriescircuits (114, 115), in parallel to the line (113), and to a ground (8).16. A circuit module with a circuit array according to one of claims 1to 15, containing a multilayer ceramic substrate (20) with integratedpassive components (21, 22, 23), which form frequency filters (13, 14,15, 16, 17), on the upper side of which a switch unit (4) is arranged,and into which the first protective device (6) is integrated.
 17. Use ofa circuit module according to claim 16 as a front-end module in a mobiletelephone.